This happened to me on a couple of occasions when I posted a new reply - the POST takes very long and in the end, I get HTTP 500, Internal Server Error message in my Firefox 3.6 (it's not a FF message, rather, it looks like a simple HTML page outputted by the web server). In Firefox, I then usually can't access forum.dokuwiki.org at all for a few moments even if I try to access the forum homepage (i.e., via normal HTTP GET). Normal functionality is restored after some time.